Marine Engine Lubrication

ABSTRACT

A two-stroke or four-stroke marine engine lubricating oil composition comprising an oil of lubricating viscosity in a major amount and (A) additives in respective minor amounts; and (B) a polymethacrylate viscosity modifier. Preferably, brightstock is completely or substantially absent from the composition.

FIELD OF THE INVENTION

This invention relates to the lubrication of 2-stroke and 4-strokemarine diesel internal combustion engines, the former usually beingreferred to as cross-head engines and the latter as trunk pistonengines. Respective lubricants therefor are usually known as marinediesel cylinder lubricants (“MDCL's”) and trunk piston engine oils(“TPEO's”).

BACKGROUND OF THE INVENTION

Cross-head engines are slow engines with a high to very high powerrange. They include two separately-lubricated parts: the piston/cylinderassembly lubricated with total-loss lubrication by a highly viscous oil(an MDCL); and the crankshaft lubricated by a less viscous lubricant,usually referred to as a system oil.

Trunk piston engines may be used in marine, power-generation and railtraction applications and have a higher speed than cross-head engines. Asingle lubricant (TPEO) is used for crankcase and cylinder lubrication.All major moving parts of the engine, i.e. the main and big endbearings, camshaft and valve gear, are lubricated by means of a pumpedcirculation system. The cylinder liners are lubricated partially bysplash lubrication and partially by oil from the circulation systemsthat finds its way to the cylinder wall through holes in the pistonskirt via the connecting rod and gudgeon pin.

It is known in the art to include brightstock in MDCL's and TPEO's,brightstock being a high viscosity oil that is highly refined anddewaxed and that is produced from residual stocks or bottoms. It may,for example, have a kinematic viscosity at 100° C. of greater than 25,usually greater than 30, mm²s⁻¹, such as a solvent-extracted,de-asphalted product from vacuum residuum generally having a kinematicviscosity at 100° C. of 28-36 mm²s⁻¹.

Brightstock is however expensive and art describes ways of replacing it.WO 99/64543 describes MDCL's formulated without brightstock and US2008/0287329 describes a TPEO containing little or no brightstock.

A problem in the art is to formulate brightstock-free MDCL's and TPEO'sat reduced cost and at the same time provide improved antiwearproperties.

SUMMARY OF THE INVENTION

It is now found that the use of polymethacrylate in an MDCL or a TPEOenables the above problem to be overcome.

Thus, the present invention provides a two-stroke or four-stroke marineengine lubricating oil composition comprising an oil of lubricatingviscosity in a major amount and

-   -   (A) additives, in respective minor amounts; and    -   (B) a viscosity modifier in the form of a polymethacrylate in an        amount in the range of 0.05-6 mass %,        wherein the composition includes less than 0.5 mass %,        preferably less than 0.1 mass %, of brightstock; preferably        brightstock is completely or substantially absent from the        composition.

In further aspects the present invention comprises:

The use of a viscosity modifier (B) to improve the anti-wear propertiesof a marine diesel cylinder lubricant of a trunk piston engine oil whichincludes less than 0.5 mass %, preferably less than 0.1 mass %, ofbrightstock; preferably brightstock is absent or is substantially absentfrom the marine diesel cylinder lubricant or the trunk piston engineoil;

A method of lubricating a cross-head marine diesel engine comprisingsupplying the composition to the piston/cylinder assembly of the engine;and

A method of lubricating a trunk piston marine diesel engine comprisingsupplying the composition to the engine.

In this specification, the following words and expressions, if and whenused, have the meanings ascribed below:

“active ingredients” or “(a.i.)” refers to additive material that is notdiluent or solvent;

“comprising” or any cognate word specifies the presence of statedfeatures, steps, or integers or components, but does not preclude thepresence or addition of one or more other features, steps, integers,components or groups thereof; the expressions “consists of” or “consistsessentially of” or cognates may be embraced within “comprises” orcognates, wherein “consists essentially of” permits inclusion ofsubstances not materially affecting the characteristics of thecomposition to which it applies;

“major amount” means 40 or 50 mass % or more of a composition;

“minor amount” means less than 50 mass % of a composition;

“TBN” means total base number as measured by ASTM D2896.

Furthermore in this specification, if and when used:

“calcium content” is as measured by ASTM 4951;

“phosphorus content” is as measured by ASTM D5185;

“sulphated ash content” is as measured by ASTM D874;

“sulphur content” is as measured by ASTM D2622;

“KV100” means kinematic viscosity at 100° C. as measured by ASTM D445.

Also, it will be understood that various components used, essential aswell as optimal and customary, may react under conditions offormulation, storage or use and that the invention also provides theproduct obtainable or obtained as a result of any such reaction.

Further, it is understood that any upper and lower quantity, range andratio limits set forth herein may be independently combined.

DETAILED DESCRIPTION OF THE INVENTION

The features of the invention will now be discussed in more detailbelow.

Oil of Lubricating Viscosity

The lubricant composition contains a major proportion of an oil oflubricating viscosity. Such lubricating oils may range in viscosity fromlight distillate mineral oils to heavy lubricating oils. Generally, theviscosity of the oil ranges from 2 to 40, such as 3 to 15, mm²/sec, asmeasured at 100° C., and a viscosity index of 80 to 100, such as 90 to95. The lubricating oil may comprise greater than 60, typically greaterthan 70. mass % of the composition.

Natural oils include animal oils and vegetable oils (e.g., castor oil,lard oil); liquid petroleum oils and hydrorefined, solvent-treated oracid-treated mineral oils of the paraffinic, naphthenic and mixedparaffinic-naphthenic types. Oils of lubricating viscosity derived fromcoal or shale also serve as useful base oils.

Synthetic lubricating oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,polybutylenes, polypropylenes, propylene-isobutylene copolymers,chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes),poly(1-decenes)); alkybenzenes (e.g., dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes);polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); andalkylated diphenyl ethers and alkylated diphenyl sulphides andderivative, analogues and homologues thereof

Alkylene oxide polymers and interpolymers and derivatives thereof wherethe terminal hydroxyl groups have been modified by esterification,etherification, etc., constitute another class of known syntheticlubricating oils. These are exemplified by polyoxyalkylene polymersprepared by polymerization of ethylene oxide or propylene oxide, and thealkyl and aryl ethers of polyoxyalkylene polymers (e.g.,methyl-polyiso-propylene glycol ether having a molecular weight of 1000or diphenyl ether of poly-ethylene glycol having a molecular weight of1000 to 1500); and mono- and polycarboxylic esters thereof, for example,the acetic acid esters, mixed C₃-C₈ fatty acid esters and C₁₃ oxo aciddiester of tetraethylene glycol.

Another suitable class of synthetic lubricating oils comprises theesters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkylsuccinic acids and alkenyl succinic acids, maleic acid, azelaic acid,suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic aciddimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with avariety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecylalcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycolmonoether, propylene glycol). Specific examples of such esters includesdibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctylsebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate,didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester oflinoleic acid dimer, and the complex ester formed by reacting one moleof sebacic acid with two moles of tetraethylene glycol and two moles of2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols and polyol esters such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol andtripentaerythritol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- orpolyaryloxysilicone oils and silicate oils comprise another useful classof synthetic lubricants; such oils include tetraethyl silicate,tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate,tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl)silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanesand poly(methylphenyl)siloxanes. Other synthetic lubricating oilsinclude liquid esters of phosphorus-containing acids (e.g., tricresylphosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid)and polymeric tetrahydrofurans.

Unrefined, refined and re-refined oils can be used in lubricants of thepresent invention. Unrefined oils are those obtained directly from anatural or synthetic source without further purification treatment. Forexample, a shale oil obtained directly from retorting operations;petroleum oil obtained directly from distillation; or ester oil obtaineddirectly from esterification and used without further treatment areunrefined oils.

Marine Diesel Cylinder Lubricant (“MDCL”)

An MDCL may employ 10-35, preferably 13-30, most preferably 16-24, mass% of a concentrate or additive package, the remainder being base stock.It preferably includes at least 50, more preferably at least 60, evenmore preferably at least 70, mass % of oil of lubricating viscositybased on the total mass of MDCL. Preferably, the MDCL has acompositional TBN (using ASTM D2896) of 40-100, such as 50-60.

The following may be mentioned as examples of typical proportions ofadditives in an MDCL.

Mass % a.i. Mass % a.i. Additive (Broad) (Preferred) detergent(s)  1-20 3-15 dispersant(s) 0.5-5   1-3 anti-wear agent(s) 0.1-1.5 0.5-1.3 pourpoint dispersant 0.03-1.15 0.05-0.1  base stock balance balance

Trunk Piston Engine Oil (“TPEO”)

A TPEO may employ 7-35, preferably 10-28, more preferably 12-24, mass %of a concentrate or additives package, the remainder being base stock.Preferably, the TPEO has a compositional TBN (using D2896) of 20-60,such as 25-55.

The following may be mentioned as typical proportions of additives in aTPEO.

Mass % a.i. Mass % a.i. Additive (Broad) (Preferred) detergent(s)0.5-12  2-8 dispersant(s) 0.5-5   1-3 anti-wear agent(s) 0.1-1.5 0.5-1.3oxidation inhibitor 0.2-2   0.5-1.5 rust inhibitor 0.03-0.15 0.05-0.1 pour point dispersant 0.03-1.15 0.05-0.1  base stock balance balance

When a plurality of additives is employed it may be desirable, althoughnot essential, to prepare one or more additive packages comprising theadditives, whereby several additives can be added simultaneously to thebase oil to form the lubricating oil composition. Dissolution of theadditive package(s) into the lubricating oil may be facilitated bysolvents and by mixing accompanied with mild heating, but this is notessential. The additive package(s) will typically be formulated tocontain the additive(s) in proper amounts to provide the desiredconcentration, and/or to carry out the intended function, in the finalformulation when the additive package(s) is/are combined with apredetermined amount of base lubricant. Thus, compounds in accordancewith the present invention may be admixed with small amounts of base oilor other compatible solvents together with other desirable additives toform additive packages containing active ingredients.

More detailed description of additive components is given below.

Detergents

A detergent is an additive that reduces formation of deposits, forexample, high-temperature varnish and lacquer deposits, in engines; ithas acid-neutralising properties and is capable of keeping finelydivided solids in suspension. It is based on metal “soaps”, that is,metal salts of acidic organic compounds, sometimes referred to assurfactants.

A detergent comprises a polar head with a long hydrophobic tail. Largeamounts of a metal base are included by reacting an excess of a metalcompound, such as an oxide or hydroxide, with an acidic gas such ascarbon dioxide to give an overbased detergent which comprisesneutralised detergent as the outer layer of a metal base (e.g.carbonate) micelle.

The detergent is preferably an alkali metal or alkaline earth metaladditive such as an overbased oil-soluble or oil-dispersible calcium,magnesium, sodium or barium salt of a surfactant selected from phenol,sulphonic acid, carboxylic acid, salicylic acid and naphthenic acid,wherein the overbasing is provided by an oil-insoluble salt of themetal, e.g. carbonate, basic carbonate, acetate, formate, hydroxide oroxalate, which is stabilised by the oil-soluble salt of the surfactant.The metal of the oil-soluble surfactant salt may be the same ordifferent from that of the metal of the oil-insoluble salt. Preferablythe metal, whether the metal of the oil-soluble or oil-insoluble salt,is calcium.

The TBN of the detergent may be low, i.e. less than 50 mg KOH/g, medium,i.e. 50-150 mg KOH/g, or high, i.e. over 150 mg KOH/g, as determined byASTM D2896. Preferably the TBN is medium or high, i.e. more than 50 TBN.More preferably, the TBN is at least 60, more preferably at least 100,more preferably at least 150, and up to 500, such as up to 350 mg KOH/g,as determined by ASTM D2896.

Anti-Oxidants

The trunk piston diesel engine lubricant composition may include atleast one anti-oxidant. The anti-oxidant may be aminic or phenolic. Asexamples of amines there may be mentioned secondary aromatic amines suchas diarylamines, for example diphenylamines wherein each phenyl group isalkyl-substituted with an alkyl group having 4 to 9 carbon atoms. Asexamples of anti-oxidants there may be mentioned hindered phenols,including mono-phenols and bis-phenols.

Preferably, the anti-oxidant, if present, is provided in the compositionin an amount of up to 3 mass %, based on the total amount of thelubricant composition.

Other additives such as pour point depressants, anti-foamants, metalrust inhibitors, pour point depressants and/or demulsifiers may beprovided, if necessary.

The terms ‘oil-soluble’ or ‘oil-dispersable’ as used herein do notnecessarily indicate that the compounds or additives are soluble,dissolvable, miscible or capable of being suspended in the oil in allproportions. These do mean, however, that they are, for instance,soluble or stably dispersible in oil to an extent sufficient to exerttheir intended effect in the environment in which the oil is employed.Moreover, the additional incorporation of other additives may alsopermit incorporation of higher levels of a particular additive, ifdesired.

The lubricant compositions of this invention comprise defined individual(i.e. separate) components that may or may not remain the samechemically before and after mixing.

It may be desirable, although not essential, to prepare one or moreadditive packages or concentrates comprising the additives, whereby theadditives can be added simultaneously to the oil of lubricatingviscosity to form the lubricating oil composition. Dissolution of theadditive package(s) into the lubricating oil may be facilitated bysolvents and by mixing accompanied with mild heating, but this is notessential. The additive package(s) will typically be formulated tocontain the additive(s) in proper amounts to provide the desiredconcentration, and/or to carry out the intended function in the finalformulation when the additive package(s) is/are combined with apredetermined amount of base lubricant.

Thus, the additives may be admixed with small amounts of base oil orother compatible solvents together with other desirable additives toform additive packages containing active ingredients in an amount, basedon the additive package, of, for example, from 2.5 to 90, preferablyfrom 5 to 75, most preferably from 8 to 60, mass % of additives in theappropriate proportions, the remainder being base oil.

The final formulations may typically contain about 5 to 40 mass % of theadditive packages(s), the remainder being base oil.

Viscosity Modifier

In this invention, as stated above, a viscosity modifier (B) isadditionally provided. Examples of ranges in the composition include0.1-6, 0.1-5, 0.1-4, 0.1-2.5, and lower limits of 0.5 and 1 mass %.

The polymethacrylate-based viscosity index improvers which may be usedin the present invention are any type of non-dispersion type ordispersion type polymethacrylate compounds which are used as viscositymodifiers for a lubricating oil.

The non-dispersion type polymethacrylate-based viscosity index improvermay be a polymer of a compound represented by the formula

CH₂═C(CH₃)COOR¹  (I)

In formula (1) R¹ is a straight chain or branched alkyl group such asmethyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, and octadecyl groups.

Specific examples of the dispersion type polymethacrylate-basedviscosity index improver are copolymers obtained by copolymerizing oneor more monomers selected from compounds represented by formula (1) withone or more nitrogen-containing monomers selected from compoundsrepresented by formulae (2) and (3)

CH₂═C(R²)COO—(R³)_(a)—X¹  (2)

CH₂═C(R⁴)X²  (3)

In formulae (2) and (3) R² and R⁴ are each independently hydrogen ormethyl. R³ is a straight chain or branched alkylene group having 1 to 18carbon atoms, such as ethylene, propylene, butylene, pentylene,hexylene, heptylene, octylene, nonylene, decylene, undecylene,dodecylene, tridecylene, tetradecylene, pentadecylene, hexadecylene,heptadecylene, and octadecylene groups; a is 0 or 1; X¹ and X² are eachindependently an amino-or heterocyclic-residue having 1 or 2 nitrogenatoms and 0 to 2 oxygen atoms. Specific examples of X¹ and X² aredimethylamino, diethylamino, dipropylamino, dibutylamino, anilino,toluidino, xylidino, acetylamino, benzoilamino, morpholino, pryrolyl,pyridyl, methylpyridyl, pyrolidinyl, piperidinyl, quinonyl,pyrrolidonyl, pyrrolidono, imidazolino, and pyrazino groups.

Specific examples of the nitrogen-containing monomers represented byformula (2) and (3) are dimethylaminomethylmethacrylate,diethylaminomethylmethacrylate, dimethylaminoethylmethacrylate,diethylaminoethylmethacrylate, 2-methyl-5-vinylpyridine,morpholinomethylmethacrylate, morpholinoethylmethacrylate,N-vinylpyrrolidone, and mixtures thereof.

The lower limit of the weight-average molecular weight of thepolymethacrylate-based viscosity modifier, which is effective inimproving the performance of an engine oil, is preferably 180,000, morepreferably 190,000. The upper limit is preferably 500,000, morepreferably 400,000.

An engine oil composition according to the present invention may containthe polymethacrylate-based viscosity modifier in such an amount that thecomposition has a kinematic viscosity at 100° C. of 4.0 to 9.3 mm²/s.

EXAMPLES

The present invention is illustrated by, but in no way limited to, thefollowing examples.

MDCL's

A set of MDCL's was formulated, each containing 20.89 mass % of the sameadditives in the proportions and having a TBN of about 70. The setcomprised a control consisting of additive and base oil; a referenceconsisting of additives, base oil and brightstock; and an inventive MDCLconsisting of additives, base oil and viscosity modifier. The additiveswere additives known in the art and used in proportions known in the artfor conferring MDCL properties. The viscosity modifier was apolymethcylate (PMA) supplied by Rohmax. The brightstock was a Group Ibright stock with a kinematic viscosity of >20 cSt at 100° C. The baseoil was a Group 1 base oil.

TPEO's

A set of TPEO's was formulated, each containing 16 mass % of the sameadditives in the same proportions and having a TBN of about 40. The setcomprised a control consisting of additives and base oil; a referenceconsisting of additives, base oil and bright stock; and an inventiveMDCL consisting of additives, base oil and viscosity modifier. Theadditives were additives known in the art and used in proportions knownin the art for conferring TPEO properties. The viscosity modifier,brightstock and base oil were used in the MDCL's.

Testing & Results

Samples of the above formulations were tested using a PCS Instrumentshigh frequency reciprocating rig (HFRR) on a standard protocolcomprising the following conditions:

-   -   120 minutes    -   20 Hz reciprocation of 1 mm stroke length    -   200 g load using standard equipment manufacturer supplied steel        substrates.

Each test was repeated two further times and the recorded wearmeasurement was the average of these values.

The HFRR data for the compositions are summarized in the table below.

TABLE Result Additive Base oil Brightstock PMA (wear Ex (mass %) (mass%) (mass %) (mass %) vol m³) TPEO Control 16 84 — — 5,584 Reference 1 1675.5 8.5 — 8,279 16 83.37 — 0.63 4,646 MDCL Control 20.89 79.11 — —33,960 Reference 2 20.89 58.89 20.22 — 3,940 20.89 77.61 — 1.5  6,792

The above results show that the use of polymethacrylate advantageouslyreduces the wear scar volume as compared to the control and referencesamples for TPEO oils. For MDCL it is clearly advantageous to includethe polymethacrylate versus using no brightstock at all.

What is claimed is:
 1. A two-stroke or four-stroke marine enginelubricating oil composition comprising an oil of lubricating viscosityin a major amount and (A) additives, in respective minor amounts; and(B) a viscosity modifier in the form of a polymethacrylate in an amountin the range of 0.05-6 mass %, wherein the composition includes lessthan 0.5 mass % of brightstock; and wherein the two-stroke marine enginelubricating oil composition has a TBN of 40 to 100 mg KOH/g, ascalculated using ASTM D2896, or the four-stroke marine enginelubricating oil composition has a TBN of 20 to 60 mg KOH/g, ascalculated using ASTM D2896.
 2. The composition as claimed in claim 1,wherein the polymethacrylate has a weight-average molecular weight of180,000 or more.
 3. The composition as claimed in claim 1, wherein thepolymethacrylate is a polymer ofCH₂═C(CH₃)COOR¹  (I) where R¹ is a straight chain or branched alkylgroup having 1-18 carbon atoms.
 4. The composition as claimed in claim3, wherein the polymethacrylate is a copolymer of a monomer of formula(I) and a N-containing monomer selected fromCH₂═C(R²)COO—(R³)_(a)—X¹ and CH₂═C(R⁴)X² where R² and R³ are eachindependently, H or CH₃; R³ is a straight chain or branched alkylenegroup having 2-18 carbon atoms; a is 0 or 1; X¹ and X² are eachindependently an amine residue or heterocyclic ring having 1 or 2 Natoms and 0-20 atoms.
 5. The composition as claimed in claim 1, in theform of a marine diesel cylinder lubricant.
 6. The composition asclaimed in claim 1, in the form of a trunk piston engine oil.
 7. Amethod of lubricating a cross-head marine diesel engine comprisingsupplying a composition as claimed in claim 1 to the piston/cylinderassembly of the engine.
 8. A method of lubricating a trunk piston marinediesel engine comprising supplying a composition as claimed in claim 1to the engine.
 9. A method of reducing the amount of brightstock in atwo-stroke or four-stroke marine engine lubricating oil compositioncomprising an oil of lubricating viscosity in a major amount and (A)additives, in respective minor amounts; the method comprising the stepof replacing, in part or in full, the brightstock with 0.05 to 6 mass %of (B) a viscosity modifier in the form of a polymethacrylate.
 10. Themethod as claimed in claim 9, wherein (B) substantially replaces thebrightstock so that the composition includes less than 0.5 mass %. 11.The method as claimed in claim 10, wherein the composition includes lessthan 0.1 mass % of brightstock.
 12. The method as claimed in claim 11,wherein the composition is completely or substantially free frombrightstock.
 13. The method as claimed in claim 9, wherein thetwo-stroke marine engine lubricating oil composition has a TBN of 40 to100 mg KOH/g, as calculated using ASTM D2896, or the four-stroke marineengine lubricating oil composition has a TBN of 20 to 60 mg KOH/g, ascalculated using ASTM D2896.